Given that most vet schools require upper level biology courses, you might want to consider getting bio done in your first year back. Also, some key advice that I wish I had known before I started at a fancy (aka, Ivy league, super competative/intense) post-bacc program, is that most schools don't care where you take your classes as long as you get A's. This issue certainly has been debated in a previous thread that you can look up (I think it's called "does prestige matter?" or something). So unless you are 100% committed to Harvard Extension, you might want to look into night science classes at other schools in the area. It might save you some sanity. Leaving my program certainly did, and I had a successful application year this year.